One of the plurality peptides to be recently discovered contains seventeen amino acids and is generally referred to as dynorphin. Dynorphin has been discovered to have potent agonist properties in guinea pig ileum and mouse vas deferens. Both dynorphin(1-13) and dynorphin(1-17) have been sequenced and synthesized. The synthetic dynorphin(1-13) product has been found to be as potent in bioassays as the naturally occurring peptide, but has been shown to be relatively weak in producing analgesia in studies with mice.
It has been reported that dynorphin(1-13), but not the shorter fragment, dynorphin(1-9), has significant effects on opiate and .beta.-endorphin-induced analgesia in naive animals. The studies have suggested that dynorphin(1-13) may interact with other analgesic opioids. Thus, it has been recently shown that dynorphin(1-13) appears to interact with morphine to significantly attenuate, or inhibit, the analgesia produced by morphine in naive animals.